Radio frequency interference, RFI, performance is essential for achieving desired radio performance defined in standardization bodies such as 3GPP and IEEE.
Integrating radio based systems into consumer electronics requires simple and fast methods to evaluate self generated radio frequency interference (RFI). Radio technologies such as WLAN (Wireless Local Area Network), WWAN (Wireless Wide Area Network) and GNSS (Global Navigation Satellite System) will be included in all kinds of devices, such as phones, notebooks, tablets, gaming consoles and a wide range of machine-to-machine (M2M) devices.
When several radio systems are integrated in one device they will interfere with each other by generating spurious emission. If RFI originated noise falls within a victim receiver bandwidth the BER (Bit error Rate) performance will be degraded, resulting in less effective throughput or other negative effects.
A modern notebook comprises several modules—or components—such as display, host, hard drive, WLAN and WWAN. For radio access system modules a self contained form factor is used with a standardized mechanical and electrical interface.
Radio devices are often realized in PCI (Peripheral Controller Interface) Express mini-card form factor mounted in a slot connector at the host. Modules can also be soldered directly on the printed circuit board (PCB) or placed as a sub-PCB connected to the host via cable. The above mentioned form factors make it simple to add extended functionality to a specific model at a low cost.
However, the design phase for consumer electronics is usually limited. Typically, a device uses standard components mounted in a limited space. Each component should fulfill specified radio performance requirements for the specific component. When several components are located closely often using shared antennas they will interfere with each other. The noise is generated from sharp clock edges, out-of band spurious emissions from co-located radios and harmonics from different clock sources. Also out-of band spurious emission from co-located radios will add in-band noise within the receiver bandwidth of a given receiver. Harmonics from clock sources and RF carrier signals are also potential sources of self interference. Micro processors, random access memories and high speed bus controllers—to name a few—are typical components generating radio interference. The noise level from these types of devices is not static. They may for instance vary as a function of processor load and memory access capacity, distance to WWAN base station.
The self generated interference level is measured for each radio sub-system based on typical use-cases. Special test equipment can be utilized to evaluate the performance degradation. In such a test, a signal emulator (e.g. Base-Station emulator) may used as signal source for the victim receiver as shown in FIG. 1.
For OTA (Over The Air) testing, anechoic chambers is required by several standard bodies such as CTIA and 3GPP for measurement of TRP (Total Radiated Power) and TRS (Total Radiated Sensitivity).
A reverberation chamber test equipment for evaluating performance degradation is known according to “Bluetest SE, Testing communication System, Performance in reverberation chamber, White paper; BTW-002 Rev A, www.bluetest.se”, downloaded from the Internet on 2011-10-25—http://www.bluetest.se/download/BTW-002_System_test_in_RC_A.pdf. The reverberation chamber constitutes an alternative to the anechoic chamber.
To be able to reduce the time to market, it is desirable to have an arrangement for the cost effective testing of RFI and in particular for an evaluation of self generated RFI.